Hurricane Irma: More than 50 dead and millions still without power

Residents returning to Florida Keys have found Hurricane Irma shredded mobile homes like soda cans and coated businesses with seaweed.

Irma, one of the most powerful Atlantic hurricanes on record before it arrived in the United States, killed 43 people in its rampage through the Caribbean and at least 12 in Florida, Georgia and South Carolina.

On Islamorada Key, one of just three islands where authorities allowed people to return yesterday, the aluminium walls of trailer homes had been ripped open by the storm.

At the Caloosa Cove Resort and Marina, concrete pilings meant to hold the dock in place had been knocked sideways and three manatees lolled in the water, drinking from an outflow pump that was spitting water from the side of the dock.

Satellite images provided by DigitalGlobe shows homes in Key West before and after Irma swept through. (AAP) ()

Local authorities told around 90,000 residents of Miami Beach and people from some parts of the Keys they could go home but warned it might not be prudent to remain there. Irma arrived in the Keys on Sunday with sustained winds of up to 215 km/h.

"It's going to take some time to let people back into their homes, particularly in the Florida Keys," Brock Long, administrator of the Federal Emergency Management Agency, said.

More than six million homes and businesses were still without power in Florida and nearby states. Florida's largest utility, Florida Power & Light, said western parts of the state might be without electricity until September 22.

The storm plunged as many as 13 million people into the dark as it dragged down power lines and blew out transformers.

Alfonso Jose Jr., 2, is floated down his flooded street by his parents as the wade through water to reach an open convenience store in the wake of Hurricane Irma in Bonita Springs. (Associated Press) ()A man paddles a kayak near a flooded home in Lithia. (Associated Press) ()Rob Brehm cleans up debris from his home as a demolished house sits across the street after Hurricane Irma in Goodland. (Associated Press) ()John Duke wades through a flooded street to try to salvage his flooded car in Jacksonville. (Associated Press) ()

The city of Jacksonville, in Florida's northeast, was recovering from heavy flooding.

Irma destroyed about one-third of the buildings on the Dutch-ruled portion of the eastern Caribbean island of St Martin en route to Florida, the Dutch Red Cross said today.

Irma hit the US soon after Hurricane Harvey, which ploughed into Houston late last month, killing about 60 and causing some $US180 billion ($A224 billion) in damage, largely through flooding.

Jean Chatelier walks through a flooded street from Hurricane Irma after retrieving his uniform from his house to return to work today at a supermarket in Fort Myers. (Associated Press) ()Lisa Borruso plays pool using a headlamp as the power remains out following Hurricane Irma at Gators' Crossroads in Naples. (Associated Press) ()A bed sits amongst the remains of its room in a home demolished from Hurricane Irma in Goodland. (Associated Press) ()

Insured property losses in Florida from Irma were expected to run from $US20 billion to $US40 billion, catastrophe modeling firm AIR Worldwide estimated.

Treasury Secretary Steven Mnuchin told a New York investor conference that the storm would ultimately boost the economy by sparking rebuilding.

The NHC is monitoring another hurricane, Jose, which was spinning in the Atlantic about 1130km west of Florida. The Atlantic hurricane season runs through November.